1. Field of the Invention
The present invention relates to an apparatus for compressing metallic chip produced from the cutting of metallic workpieces (hereinafter, referred to as the "chip"), and particularly to the art of downsizing the apparatus and improving the life expectancy of the same.
2. Related Art Statement
There is known a chip compressing device which includes a housing having two holes extending perpendicularly to each other, a chip compressing ram fitted in one of the two holes (hereinafter, referred to as the ram-receive hole) such that the ram is movable in an axial direction of the one hole, a movable member fitted in the other hole (hereinafter, referred to as the movable-member-receive hole) such that the movable member is movable in an axial direction of the other hole, and a movable-member moving device which moves the movable member to an operative position where the movable member closes one of opposite open ends of the ram-receiver hole that is nearer to the movable-member-receive hole, and cooperates with the ram-receive hole to define a chip storing space having a bottom wall, and to a retracted position away from the operative position. In the state in which the chip is stored in the chip storing space, the compressing ram is moved downward and cooperates with the housing and the movable member to compress the metallic chip. After the compressing, the movable member is moved or retracted to the retracted position, to open the bottom of the chip storing space, and the ram is further moved downward to push the compressed chip out of the ram-receive hole into the movable-member-receive hole. Then, the movable member is moved to the operative position, to push the compressed chip out of the movable-member-receive hole.
However, the prior chip compressing device has various problems. One of them is that the movable-member moving device that moves the movable member to the operative and retracted positions must produce a great operation force, which leads to increasing the size, and the production cost, of the chip compressing device. When the chip is compressed, the movable member is pressed by the chip compressing ram via the chip. Even after the ram is moved away from the compressed chip following the compressing, the movable member remains pressed by the compressed chip. A frictional force is produced between the chip and the housing. When the chip is compressed, the frictional force acts in a direction opposite to the direction in which the chip is compressed by the ram, so that the frictional force decreases the force of the ram to press the movable member via the chip. After the compressing, the frictional force acts in the direction in which to press the movable member, so that the chip presses the movable member with a force equal to the frictional force.
This pressing force is produced because the housing supports the chip with the frictional force, and is great. Once the chip compressing ram is moved away from the compressed chip, the compressed chip expands, i.e., produces a spring back. Since, however, the open end of the ram-receive hole is closed by the movable member and accordingly the compressed chip cannot expand into the movable-member-receive hole, it expands in a direction opposite to a direction toward the movable member. Thus, there occurs a frictional force, between the chip and the housing, in the direction toward the movable member to resist the spring back of the chip. The spring back of the compressed chip stops at a position where the force to produce the spring back is counterbalanced by the frictional force and at that timing the frictional force becomes maximum. Thus, the movable member is pressed by the compressed chip with a force equal to the maximum frictional force. Therefore, the movement of the movable member to the retracted position needs a force greater than the sum of (a) the product of the force equal to the maximum frictional force and a friction coefficient between the chip and the movable member and (2) the product of the force equal to the maximum frictional force and a friction coefficient between the housing and the movable member. Assuming that the chip compressing force of the ram is not changed, the maximum frictional force increases as the amount of chip compressed increases. Thus, the movable-member moving device must produce a great operation force to move the movable member, which leads to increasing the size, and the production cost, of the chip compressing device.
Another problem with the prior chip compressing device is that in some cases the chip compressing ram is moved downward in the state in which no or little chip is stored in the chip storing space, so that the ram and the movable member are damaged. If the ram is moved downward in the state in which the chip storing space is substantially empty and only a little amount of chip, a shot ball which had been adhered to a workpiece, and/or a broken piece of a tip of a cutting tool remain on the movable member, the ram presses those remains against the movable member and accordingly local stresses are produced in the ram and the movable member. Thus, the ram and the movable member are scarred. In the case where the remains such as the chip are softer than the ram and the movable member, it does not seem that the ram or the movable member is damaged but, in fact, they are damaged.
If the ram or the movable member is scarred, it swells around the scar in its outer surface. In the case where the movable member has a scar and a swollen portion therearound in its outer surface, the frictional force produced between the movable member and the chip increases, which leads to needing a greater operational force of the movable-member moving device. In addition, in the case where either the movable member or the ram has a swollen portion around a scar in its outer surface, it may have, at the end of the outer surface, a projecting portion, which may damage an inner surface of the ram-receive hole or an inner surface of the movable-member-receive hole. In a particular case where the amount of projection of the projecting portion from the outer surface exceeds a clearance provided between the movable member and the movable-member-receive hole, or a clearance provided between the ram and the ram-receive hole, the resistance to the movement of the movable member relative to the movable-member-receive hole, or the resistance to the movement of the ram relative to the ram-receive hole excessively increases, which leads to even stopping the movement of the movable member by the movable-member moving device of a small size.